The advances in our ability to do genetic manipulations in the microbial biochemical pathways accompanied by improvements in fermentation process technology have made it possible to produce commercially significant quantities of succinic acid using agricultural and forestry renewable feedstocks. All of the microbial organisms engineered to produce succinic acid reach their maximum productivity within a narrow pH range. For this reason, during the fermentative production of succinic acid, the pH of the fermentation medium is kept at near neutral pH by means of compensating the drop in the pH of the medium with the addition of certain neutralizing base compounds. This results in the accumulation of succinic acid in the fermentation medium in the form of a basic salt of succinic acid. Thus depending on the nature of the neutralizing base used, the succinic acid accumulates in the fermentation medium as sodium or potassium or calcium or ammonium succinate. Therefore, further downstream processing of the fermentation broth is required to extract the pure succinic acid from the fermentation broth containing a basic salt of succinic acid. A downstream processing method that recovers succinic acid from the fermentation broth along with the release of the neutralizing agent is desirable in the succinic acid manufacturing in a commercially successful way.
Several different approaches have been followed to purify the organic acids from fermentation broth including precipitation, steam distillation, liquid-liquid extraction, counter-current extraction, esterification, and a combination of electrodialysis and extraction. In general, the fermentation broth is subjected to microfiltration and ultrafiltration to remove cellular debris before subjecting to any specific process to recover succinic acid.
A number of methods have been reported for the recovery of succinic acid from the fermentation broth containing a basic salt of succinic acid. All these known processes for the recovery of succinic acid from fermentation broth are found to be lengthy and expensive for the production of succinic acid from fermentation broth in a commercial scale.
U.S. Pat. No. 5,034,105 assigned to Michigan Biotechnology Institute provides a process for preparing succinic acid from a fermentation broth containing sodium succinate. This process comprises steps of subjecting the broth to conventional electrodialysis to prepare an aqueous but unsaturated succinate solution, subjecting the unsaturated succinate solution to water splitting electrodialysis to produce a supersaturated succinic acid solution and then crystallizing the succinic acid from the supersaturated solution. This process is not suitable for the purification of succinic acid from the fermentation broth in a large scale as evidenced by the lack of commercial exploitation of this process during the last twenty years of its existence.
U.S. Pat. Nos. 5,958,744 and 6,265,190 assigned to Applied CarboChemicals provide a method for recovering succinic acid from fermentation broth containing calcium succinate. According to this method, the fermentation broth is acidified with the addition of sulfuric acid. As a result of this acidification process, the succinate anion is released from calcium succinate, gets protonated and the resulting succinic acid precipitates out of the fermentation broth. The resulting precipitate is filtered and washed with alcohol to obtain succinic acid. It remains to be seen whether the succinic acid thus produced would satisfy the required level of purity. In addition, the disposal of calcium sulfate (gypsum) poses an environmental concern.
A recently published United States Patent Application Publication No. U.S. 2010/0297715 assigned to Roquette Freres describes a process for separating and purifying succinic acid from fermentation broth containing magnesium succinate. The separation process described in this published patent application is complicated and expensive. The separation process involves bipolar electrodialysis, evaporative crystallization, and high temperature treatment to recover the reagents for recycling purpose. As a result of these process steps involved in the recovery of succinic acid from fermentation broth, the cost of production of succinic acid using this process in a commercial scale is going to be very expensive.
A recent U.S. Patent Application Publication No. 2009/0137825 assigned to BASF has disclosed a reactive distillation process for esterifying succinic acid from fermentation broth. However, this Patent Application Publication does not provide any actual method for recovering succinic acid from fermentation broth that has been reduced to practice.
A number of efforts have also been made to recover carboxylic acid from the fermentation broth using the process involving ion exchange resins. The ion exchange resins are used in two different ways in the separation of carboxylic acids from the fermentation broth comprising carboxylic acid salts. According to one method, the ion exchange resins are used in the ion exclusion mode. In another method, the ion exchange resins chemically interact with the salts of carboxylic acid in the fermentation broth to achieve the separation of the carboxylic acid from the carboxylic acid salts. The first method is referred as ion exclusion chromatography and the second method is known as ion exchange chromatography.
U.S. Pat. No. 5,132,456 provides a method for recovering carboxylic acid from aqueous feedstock in which the carboxylic acid is first adsorbed onto a basic solid adsorbent or moderately basic ion exchange resin, and then released from the adsorbent by treating it with aqueous alkylamine or ammonia leading to the formation of alkylammonium or ammonium carboxylate which is decomposed to the desired carboxylic acid and the alkylamine or ammonia.
U.S. Pat. No. 5,143,834 provides a method for recovering succinic acid from fermentation broth using desalting electrolysis and water-splitting electrolysis followed by a strongly acidic ion exchanger to remove any sodium or other cations and a weakly basic ion exchanger in the free base form to remove any sulfate ion or sulfuric acid to obtain a highly purified succinic acid product.
U.S. Pat. No. 5,168,055 provides a method for recovering succinic acid from fermentation broth containing calcium succinate. In the first stage, the fermentation broth is acidified to release succinic acid from calcium succinate. The succinic acid thus released is passed through a strongly acidic ion exchange resin and a weakly basic ion exchanger to obtain a highly purified succinic acid product. During the passage through the cation exchanger, calcium and other cations are removed. During the subsequent passage through a second column containing anionic exchange resin, the anionic impurities such as sulfate and other nitrogenous impurities are removed.
U.S. Pat. No. 5,641,406 provides a method for extracting pure lactic acid from fermentation liquors containing lactic acid salt by ion exchange chromatography on a strongly acidic cation exchange resin. In the first stage of this method, the lactic acid salt is converted into free acid by means of genuine ion exchange in one or more “preliminary columns” containing weakly acidic cation exchanger in H+ form. In the second stage of this method, the free lactic acid is separated from the carbohydrates and other impurities present in the fermentation solution by using a strongly acidic ion exchange resin in one or more “separation columns.” The process is carried out at temperature higher than 50° C. and preferably between 70° C. to 80° C.
U.S. Pat. Nos. 5,068,418 and 5,068,419 provide a method for the separation of an organic acid from a fermentation broth using an adsorbent comprising a water-insoluble macro reticular or gel type weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups or a strongly basic anionic exchange resin possessing quaternary amine functional groups. The organic acid is desorbed from the ion exchange resin with water or dilute inorganic acid like sulfuric acid.
U.S. Pat. No. 5,786,185 provides an improved fermentation process for producing lactic acid. As per this process, the fermentation broth comprising free lactic acid is contacted with an effective amount of solid-phase polymer containing pyridine groups to adsorb the lactic acid as it is accumulated and returning the treated fluid fermentation broth back to the fermentation vessel.
U.S. Pat. No. 6,160,173 describes the use of water immiscible anion exchanger to recover lactic acid from a feed solution comprising lactic acid and lactic acid salt mixture. In the first step, the feed solution is contacted with an anion exchanger and an anion exchanger-lactic acid adduct is formed. From this anion exchanger-lactic acid adduct, the lactic acid ester or amine is produced through condensation reaction.
U.S. Pat. No. 6,280,985 assigned to Roquette Freres discloses a method for separation and purification of lactic acid from a fermentation broth using an ion exclusion chromatography with cation exchange resin. This method involves several unit operations besides chromatographic separation through a cation exchange resin. Thus, the original fermentation broth is concentrated in the first stage followed by acidification with concentrated acid to reach a free lactic acid/ammonium lactate ratio of 85/15. The acidified broth is passed through cation exchange resin of the polystyrene sulfonic acid type cross-linked with at least 4% of divinylbenezene to obtain a fraction that has a maximum of 25% lactic acid salts. All the impurities such as unconsumed sugars and proteins and of the inorganic acid salts of the type with polyvalent ions calcium, magnesium and any base corresponding to any dissociated lactic acid salt in the fermentation broth are removed in the first fraction by elution with water. The next fraction contains lactic acid in the free from and at most 25% by dry weight of lactic acid salt present in the original fermentation broth. This fraction is further subjected to bipolar fractionating electrodialysis to obtain purified, concentrated lactic acid.
U.S. Pat. No. 6,284,904 discloses a method for purification of organic acids using anion exchange chromatography in which the organic acid such as succinic acid is bound to the anion resin followed by displacement of the organic acid by a strong basic anion solution or an acid having a pKa lower than that of the organic acid bound to the anion resin.
U.S. Pat. No. 6,319,382 teaches a method for recovering lactic acid from a fermentation broth containing ammonium lactate wherein the said method comprises steps of nanofiltration, ion exchange using a chelating resin that primarily removes the divalent cations such as calcium and magnesium and a final two-step electrodialysis procedure.
U.S. Pat. No. 7,238,837 provides a method for recovering lactic acid from aqueous solution containing lactate salt with a conversion efficiency of 56% of the sodium lactate to lactic acid through a method using cation exchange resin.
U.S. Pat. No. 7,439,392 provides a method for separating citric acid from a fermentation broth by using an adsorbent comprising a water-insoluble, macro reticular or gel, strongly or weakly basic anionic exchanger resin possessing quaternary or tertiary amine functional groups, anionic exchange resin having a cross-linked acrylic or styrene resin matrix and a desorbent comprising water or dilute sulfuric acid. The pH of the feed is maintained below the first ionization constant (pKa1) of citric acid to maintain selectivity.
U.S. Patent Application Publication No. 2006/0276674 describes a method for purifying succinic acid from fermentation broth. According to this method, the impurities in a succinic acid containing liquid could be efficiently removed by combining ion-exchange using a certain amount of an H-type strongly acidic cation-exchange resin with a crystallization process to produce high purity succinic acid in good yield.
International application No. WO 2007/040458 published under the Patent Cooperation Treaty provides a method for removing cationic and anionic impurities using ion exchange resin in the process of recovering lactic acid from fermentation broth containing lactic acid. The ammonium ions were removed using a strong cationic exchange resin and the anion exchange resin was used to remove sulfate impurity.
International patent application No. WO 98/30712 published under the Patent Cooperation Treaty and assigned to Amylum Belgium provides a method for recovering crystalline aspartic acid from ammonium aspartate using a cation exchanger resin.
Various methods tested so far to recover organic acids from fermentation broth have presented limitations and thus offer opportunities for improvement. Thus the objective of the present invention is to provide a commercially viable process for recovering succinic acid from a fermentation broth comprising ammonium succinate.